A Ti bulk disk (99.9% purity, 2 in. diameter) was adapted for the
sputtering target. Ti thin films were deposited on the Si substrate
(2.5 × 5 cm2) using a DC magnetron sputtering system. In order to
remove the native oxide layer of Si, the Si substrates were dipped in
hydrofluoric acid (HF) solution for 30 s, and then they were ultrasonically
rinsed in acetone, ethanol, and deionized water (DI) and dried
at room temperature before being introduced into the vacuum chamber.
Next, the Si substrate was placed in the magnetron sputtering